Conventionally, a dental cement has been used not only as cementation/adhesion in crown prosthetic materials represented by metal materials such as inlay, onlay, crown and the like but also in many dental applications such as filler, lining and base materials, cementation/adhesion for orthodontic brackets and bands and the like, temporary filling materials, temporary cementing materials, sealant, root canal filling materials, core construction materials and other preventive dentistry related materials.
In addition, regardless of many types of dental cement, all of the dental cement have advantages and disadvantages in operations and properties and, therefore, applications are determined depending on the advantages and disadvantages.
In the past, zinc phosphate cement which comprises mainly zinc oxide as a powder and an orthophosphoric acid aqueous solution as a liquid was mainly used as a cementing material in crown prosthetic materials such as molded metal materials. However, this kind of cement has disadvantages that a great pulp irritation occurs due to phosphoric acid at an earlier stage of setting, that properties vary depending on a mixing temperature because a setting reaction is an exothermic reaction, that prosthetic appliances are hold via mechanical interlock, and the like.
A carboxylate cement which comprises mainly zinc oxide as a powder and a poly(carboxylic acid) aqueous solution as a liquid sets by chelate of zinc ions released from the powder when the powder is eroded with the liquid and carboxyl groups which are side groups of the poly(carboxylic acid) comprised in the liquid. Since at the same time those carboxyl groups also chelate with metal elements such as calcium existing in tooth substance, this cement also has adhesiveness to tooth substance. This cement has an advantage that a pulp irritation is smaller and a disadvantage that a mechanical strength is lower comparing to the zinc phosphate cement.
A eugenol cement which comprises mainly zinc oxide as a powder and a eugenol oil as a liquid has an advantage as having analgesic, sedative and antiphlogistic effects to oral diseases, but its application is limited to temporary sealing or temporary cementation because its mechanical strength is low and has poor durability in oral cavities.
A resin cement comprising mainly an organic polymer or an inorganic filler as a powder and an acrylic polymerizable monomer as a liquid, and at least either of them contains a polymerization catalyst has adhesion to tooth substance and mechanical properties which are much more excellent than those of other cement.
However, it has a disadvantage that complicated pretreatments such as etching and primer applying to materials to be used are necessary, and that biocompatibility is poor, and the like.
In addition, since this cement cures via a polymerization reaction of polymerizable monomers, it is liable to undergo polymerization inhibition, and further it has a disadvantage that an unpolymerized layer of the polymerizable monomer exists on the surface of a cured resin cement. The existence of this unpolymerized layer causes discoloration or coloring in the cured resin cement, and generation of secondary caries in tooth substance around an unpolymerized layer to which bacteria adhered. In order to eliminate or reduce this unpolymerized layer, complicated handling such as covering the surface with an oxybarrier to block oxygen, irradiating with light and the like is required not only in pretreatment but also during and after a curing process.
A glass ionomer cement which comprises mainly an aluminosilicate glass containing elements such as fluorine, calcium, and the like as a powder and a poly(carboxylic acid) aqueous solution as a liquid exhibits a curing behavior similar to that of a carboxylate cement although types of the powder are different from each other.
The glass ionomer cement cures by chelate of calcium ions and aluminum ions released from the powder when the powder is eroded with the liquid and carboxyl groups which are side groups of the poly(carboxylic acid) comprised in the liquid.
Since those carboxyl groups also chelate with tooth substance, this cement also has adhesiveness to tooth substance. This cement shows a smaller pulp irritation and, thus, this glass ionomer cement is also excellent in biocompatibility.
Since the glass ionomer cement has excellent transparency which cannot be observed in other cements and a high mechanical strength, its application extends from merely use as adhesives to use as filling materials.
Further, the glass ionomer cement can persistently sustained-release a trace of fluorine from the set cement and has preventive effects such as suppression and prevention of secondary caries and reinforcement of tooth substance. Therefore, it is used as a preventive material.
For this glass ionomer cement, details are described in JP 54-21858A, JP 54-10010A, JP 61-50989A, JP 2-62525A and the like.
Although the glass ionomer cement has many advantages as described above, there is a disadvantage, so-called water sensitivity, that when a surface of the cement touches to water during setting, it dissolves in water and becomes cloudy. In order to reduce the water sensitivity as much as possible, it is required to set a cement immediately after applying it in an oral cavity, by shortening a time period (a setting time) when takes from applying in the oral cavity to setting.
Moreover, complicated procedure to mix a powder and a liquid are needed for the glass ionomer cement, and mixed status varies depending on operator's procedure carrying out the mixing procedure and their skill. Therefore, it is impossible to obtain stable properties. In order to obtain stable properties, it is required to sufficiently mix by lengthening a time period (a procedure time) from the onset of mixing to application in an oral cavity as long as possible.
However, since shortening a setting time and lengthening a procedure time conflict with each other and react on each other, it has been a great problem to obtain both an ideal long procedure time and an ideal short setting time. Accordingly, there are reported many technical attempts to invest a glass ionomer cement with a short setting time to set immediately after applying in an oral cavity before touching with water with maintaining a long procedure time to carry out a sufficient mixing.
For example, as attempts to glass compositions, disclosed are “an alkaline earth metal aluminofluorosilicate salt glass comprising strontium and a cement composition containing the same” in JP 63-182238A, “a glass composition comprising specific element components for use in a glass ionomer cement” in JP 61-215234A, “a glass powder comprising ZrO2 and ZnO for a glass ionomer cement” in JP 2-275731A, “a lanthanum strontium fluoroaluminosilicate glass powder” in JP 5-331017A, “a fluoroaluminosilicate glass powder free of ions of alkali metals and specific alkaline earth metals” in JP 63-201038A, and the like.
As attempts to addition of the third components to a powder or a liquid, disclosed are “a dental cement composition comprising a water-insoluble tannic acid derivative” in JP 60-34903A and JP 63-10128A, “a dental cement setting solution of an acrylic acid-maleic acid copolymer comprising soluble organic carboxylic acid and a fluoro complex salt” in JP 59-46924A, “a dental cement setting solution of poly(acrylic acid) or copolymer of acrylic acid comprising an inorganic acid” in JP 56-37964A, “a dental cement setting solution of an acrylic acid-maleic acid copolymer comprising a fluoro complex salt and tartaric acid” in JP 59-38926A, “a dental cement setting solution comprising tetrahydrofurantetracarboxyl acid” in JP 59-24128A and JP 59-23285A, “a method for adding tartaric acid in a dental cement” in JP 55-8019A, and the like.
As attempts to treatment of a glass surface, disclosed are “a method for treating a surface of a glass powder with fluoride” in JP 3-59041A, “a method for delaying a setting reaction with poly(carboxylic acid) by washing a glass powder with acids to eliminate calcium and the like existing around the surface of the powder” in JP 59-5536A and JP 2-39465A, “a method for treating a surface of a glass powder by adding carboxylic acid in fine grinding glass lumps” in JP63-225567A, “a method for heat-treating a glass powder surface with carboxylic acid” in Japan Patent No. 2796461, and the like.
By these attempts, in any cases, some extent of improvements were observed with respect to water sensitivity, but prevention of water sensitivity has not been achieved. In addition, mixing procedure of a powder and a liquid is still complicated and, many problems remain that properties are influenced by differences in operators and their skills.
In addition, many reports are currently disclosed on cement compositions in which adhesion to tooth substance is improved by incorporating an acid-base reaction, which is a setting reaction of a glass ionomer cement without primer treatments required in use of a resin cement.
For example, disclosed are “a cement composition comprising a monomer having a polymerizable group and an ionic group at a side chain in the molecule” in JP 6-70088A and Japan Patent No. 2588702, JP 62-149707A and the like, “a dental cement composition free of water which essentially comprises a polymer of α-β unsaturated carboxylic acid and an inorganic component chelate with the polymer” in Japanese Patent No. 3542683 and JP 3-47107, and the like.
The above reports describe that due to incorporation of a monomer having a polymerizable group and an ionic group at a side chain in the molecule or a polymer of α-β unsaturated carboxylic acid into a cement composition, acidic groups in respective molecules cause an acid-base reaction with metal elements existing in the tooth substance such as calcium to improve adhesion to tooth substance.
However, in components constituting the cement, since water is not comprised as an essential component, an acid-base reaction does not occur in the inside of the cement composition and, accordingly, they differ from a glass ionomer cement in the structural aspect. Thus, properties other than adhesion to tooth substance which the glass ionomer cements have are not exerted.
These cement compositions are intended to incorporate water into the inside of the cement compositions by water absorption of the composition after curing to cause a secondary acid-base reaction and, a structural change also occurs accompanying the reaction. Therefore, material durability is concerned.
Recently, many reports are disclosed on a cement composition comprising a polymerizable monomer and a polymerization catalyst in addition to components constituting a glass ionomer cement (water, a polymer of α-β unsaturated carboxylic acid, fluoroaluminosilicate glass), and a cement composition comprising a monomer having an ionic group and a polymerizable group in its side chain instead of a polymer of α-β unsaturated carboxylic acid as a component constituting a glass ionomer cement, and further comprising a polymerizable monomer and a polymerizing catalyst.
For example, disclosed are “a cement composition comprising a monomer having an ionic group and a polymerizable group in its side chain” in Japan Patent No. 2869078 and JP 1-308855A, “a cement composition comprising a polymerizable monomer in addition to components constituting a glass ionomer cement” in JP 6-27047A, Japan Patent No. 3288698, JP 8-26925A, JP 8-301717A, JP 2000-26225A and JP 2002-87917A.
These kinds of cement compositions are called as a resin-modified glass ionomer cement and, as a curing mechanism, polymerization reactions of many types of monomers with chemical polymerization catalysts and photopolymerization catalysts are also adopted in addition to an essential reaction, an acid-base reaction, of a conventional glass ionomer cement. Consequently, even when water touches during curing, water sensitivity that a cured product becomes cloudy and brittle has been prevented and, their mechanical properties such as a bending strength and the like have been greatly improved. Further, some have not only adhesion to tooth substance such as an enamel, a dentin and the like but also adhesion to a metal, a porcelain, a composite resin and the like and, thus, they become significantly advanced materials.
However, since these cement compositions contain polymerizable monomers as a liquid component, they have disadvantages which are not observed in a glass ionomer cement, that polymerization is inhibited with oxygen during curing to generate an unpolymerized layer on a surface of a cured cement composition similar to that of a resin cement.
Similar to a conventional glass ionomer cement, a resin-modified glass ionomer cement cannot be prepared in a form of one package type based on the relationship between constituting components involving in an acid-base reaction, they should be prepared in a form of a divided package type, such as a powder-liquid type, a powder-paste type, a liquid-paste type, a paste-paste type and the like; and any glass ionomer cement is prepared mainly in a form of a powder-liquid type.
In a form of a powder-liquid type, a divisional mixing process, in which a powder is divided and mixed with a liquid stepwise upon its use, is generally carried out and mixing, which is a process repeating smear mixture thinly on a paper mixing plate to uniformly spread at a final stage of mixing, is also required in order to exert stable properties. These sequential processes are easy for skilled operators, but are difficult for operators with a little experience.
Further, in a resin-modified glass ionomer cement, since the viscosity of the liquid becomes high because the liquid contains a polymerizable monomer, miscibility of the powder and the liquid becomes worse to make mixing difficult. Moreover, a ratio between the powder and the liquid varies due to weighing variation when the powder is weighed on a measure and, therefore, intended properties or stable properties cannot be obtained.
Accordingly, reports are recently disclosed regarding the conventional glass ionomer cement or resin-modified glass ionomer cement in a two paste-type which is easy to mix regardless of operator's experience and skill by reducing complicated procedure such as weighing and divisional mixing as much as possible.
For example, disclosed is “the conventional glass ionomer cement composition in a two paste-type which comprises a polymer of α-β unsaturated carboxyl acid and water as a first paste, and a fluoroaluminosilicate glass powder, water and a water-soluble thickener as a second paste” in JP 2003-183112A. In this report, the second paste whose main component is water comprises a water-soluble thickener because a viscosity is invested to improve handling without using a polymerizable monomer. This cement composition is excellent in handling such as mixing because it is in a form of a two paste-type, but its mechanical strength deteriorates by influence of the water-soluble thickener. In addition, since the thickener is water-soluble, it inhibits the acid-base reaction to delay a setting time and, thereby, a disadvantage of the conventional glass ionomer cement, water sensitivity, tends to become worse.
JP 11-228327A discloses “a cement composition comprising a polymer of α-β unsaturated carboxylic acid, water and a filler material which does not react with the polymer of α-β unsaturated carboxylic acid as a first paste and a fluoroaluminosilicate glass and a polymerizable monomer free of an acidic group as a second paste”. In this cement composition, it is essential that constituting components causing an acid-base reaction, water and a polymer of α-β unsaturated carboxylic acid, are contained only in the first paste and a fluoroaluminosilicate glass is contained only in the second paste. In addition, in the first paste, the polymer of α-β unsaturated carboxylic acid coexists in a state where it and water are soluble to each other.
JP 2000-513339A discloses “a multiple liquid type ionomer cement comprising an organic composition which contains a polymerizable hydrophilic component and an acid functional compound (a polymer) and is substantially free of water, wherein they are soluble to each other, and an aqueous composition, which contains water and an aqueous component which is soluble to water and also disclosed is that an acid reactive filler may be comprised in any of compositions”.
In this multiple liquid type ionomer cement, it is essential that the acid functional compound (a polymer) which is an acid-base reactive constituting components is contained only in the organic composition and water is contained only in the aqueous composition, respectively, and the acid reactive filler is contained at least one of the compositions. Further, in the organic composition, the acid functional compound (a polymer) coexists in a state where it and the hydrophilic component are soluble to each other.
However, according to constitutions of the components comprised in the cement compositions disclosed in JP 11-228327A and JP 2000-513339A, since the acid-base reaction and the polymerization reaction do not occur with good balance, it is difficult to manifest characteristic properties from a glass ionomer cement, adhesion to tooth substance, surface curability, biocompatibility and fluorine sustained-releasabilty resulting in materials having properties similar to those of resin cement. In addition, in any of the cement compositions, a polymer of α-β unsaturated carboxylic acid or an acid functional compound (a polymer) involving in the acid-base reaction respectively is comprised in a soluble state. When the cement composition is cured in this state, polymerization is inhibited with oxygen during curing similar to a resin cement to form an unpolymerized layer on a surface of the cured cement. This unpolymerized layer may cause discoloration or coloration, alternatively bacteria may attach to this unpolymerized layer to cause secondary caries in the tooth substance around the area thereof.
[Patent Document 1] JP 54-21858A
[Patent Document 2] JP 54-10010A
[Patent Document 3] JP 61-50989A
[Patent Document 4] JP 2-62625A
[Patent Document 5] JP 63-182238A
[Patent Document 6] JP 61-215234A
[Patent Document 7] JP 2-275731A
[Patent Document 8] JP 5-331017A
[Patent Document 9] JP 63-201038A
[Patent Document 10] JP 60-34903A
[Patent Document 11] JP 63-10128A
[Patent Document 12] JP 59-46924A
[Patent Document 13] JP 56-37964A
[Patent Document 14] JP 59-38926A
[Patent Document 15] JP 59-24128A
[Patent Document 16] JP 59-23285A
[Patent Document 17] JP 55-8019A
[Patent Document 18] JP 3-59041A
[Patent Document 19] JP 59-5536A
[Patent Document 20] JP 2-39465A
[Patent Document 21] JP 63-225567A
[Patent Document 22] Japan Patent No. 2796461
[Patent Document 23] JP 6-70088A
[Patent Document 24] Japan Patent No. 2588702
[Patent Document 25] JP 62-149707A
[Patent Document 26] Japan Patent No. 3542683
[Patent Document 27] JP 3-47107A
[Patent Document 28] Japan Patent No. 2869078
[Patent Document 29] JP 1-308855A
[Patent Document 30] JP 6-27047A
[Patent Document 31] Japan Patent No. 3288698
[Patent Document 32] JP 8-26925A
[Patent Document 33] JP 8-301717A
[Patent Document 34] JP 2000-26225A
[Patent Document 35] JP 2002-87917A
[Patent Document 36] JP 2003-183112A.
[Patent Document 37] JP 11-228327A
[Patent Document 38] JP 2000-513339A